Information on the nature and structure of the macromolecules involved in fertilization is minimal. In an attempt to understand sperm-egg interactions on a molecular basis, it is proposed to: 1) determine the number and the chemical nature of the macromolecules in extraoval integuments, 2) elucidate the molecular structure of these macromolecules, 3) define the role these macromolecules play in fertilization and in the life of gametes and the developing embryo, 4) determine those agents in a spermatozoan responsible for penetration of the extraoval integuments and fusion with the egg plasma membrane, 5) define on a molecular basis the nature of the vitelline and fertilization envelopes as an approach to understanding the block to polyspermy, and 6) identify and characterize the agents responsible for the "releasing" of an embryo from its extraoval integuments at the time of "hatching". These research objectives will be attained through a biochemical approach employing the isolation of the macromolecules involved, their physicochemical characterization, and the reconstruction of the supramolecular structures involved to build a molecular model of sperm-egg interactions from which we should be able to better understand the process of fertilization. Our investigations will employ the frog Xenopus laevis as this organism is especially amenable for the studies suggested here.